Find a Word Along One Fixed Direction in a Grid

Determine whether a word appears in a letter grid along one straight direction. After choosing a starting cell and direction, keep that same direction for every subsequent letter. Do not turn, jump, wrap around, or revisit a prior cell.

Implement word_exists(board: string[], word: string) -> bool.

Constraints & Assumptions

• The board is rectangular, with 1 through 100 rows and columns. All characters are uppercase ASCII letters.
• The word has 1 through 100 uppercase letters.
• This practice version permits all eight nonzero adjacent directions: horizontal, vertical, and diagonal, in either orientation. The source explicitly fixes straight-line movement but does not enumerate the permitted directions.
• A one-letter word is present if any board cell contains it.
• A path must remain inside the board for its entire length.
• This is a straight-line word-search game, not a path that may change direction after each letter.

Examples

board = ["ABC","DEF","GHI"]
word = "AEI"
result = true

board = ["ABC","DEF","GHI"]
word = "ABE"
result = false

ABE would require turning after the second letter, which is not allowed.